Wireless mobile communication networks are ubiquitous in many parts of the world. As technologies advance, improvements in network capacity, speed, bandwidth, latency, flexibility, and overall sophistication continue to improve. This results in a succession of versions, or revisions, of technical specifications for a given protocol or access technology, each version adding capabilities, such as advanced operating modes (e.g., discontinuous operations for power savings), multiple antennas, multiple carriers, different duplex modes, and the like.
One advanced feature of many third-generation wireless communication protocols is the provision for multiple signal carrier frequencies, or “carriers,” known in the art as carrier aggregation (CA). By sending and receiving traffic on more than one carrier, networks can dramatically increase the communication bandwidth to suitably-equipped User Equipment (UE). In CA, a primary downlink and uplink carrier are defined for each UE, and one or more secondary carriers (downlink, uplink, or both) may additionally be configured.
In modern wireless networks, optimal conditions are achieved by adaptive operation. That is, parameters such as signal strength, data rate, modulation and coding, and the like, are adaptively tailored to the present state or condition of the network and the air interface. This requires UE to regularly perform measurements of various parameters, such as received signal strength, channel quality, interference, and the like, and report these measurements back to the network. Such measurements are also used for mobility management—such as initiating a handover of a UE from one serving network node to another based on the nodes' relative signal strengths as experienced by the UE. Thus, the feedback of measurements from UE to the network is an important part of network operations. Furthermore, these measurements must ideally be reported at fairly short intervals, since network operating conditions change constantly as the UE move around.
Some UE parameter measurements require the UE to tune to a different frequency than that of its downlink or uplink carrier. Since conventional UEs include circuits implementing only one receiver and one transmitter chain, measurement gaps are defined by most protocol technical specifications. During predetermined measurement gaps, the UE may tune to a different frequency and perform measurements, then retune to the uplink carrier frequency to report the measurements to the network. During the measurement gaps, the UE cannot receive traffic on its downlink carrier, and cannot transmit to the network on its uplink carrier.
UE capable of carrier aggregation (CA) must be able to receive and process (and/or transmit on) two or more carriers at a time. Thus, a CA-capable UE either has a wide bandwidth receiver, for receiving two closely-spaced (in frequency) carriers, or it has two or more receiver chains, each capable of tuning to a different carrier. Some CA-capable UE are even capable of operation with carriers on different Radio Access Technologies (RAT), known as inter-RAT carriers. Most wireless protocols implementing CA specify that all UE measurements are reported to the network on the primary uplink carrier.
While wideband receiver UEs may be able to perform measurements on closely spaced carriers (i.e., intra-band) without measurement gaps on the primary carrier, they may still require measurement gaps to perform measurements on carriers separated from their primary downlink/uplink carriers (inter-band), or carriers in a different RAT (inter-RAT). Some measurements, such obtaining and reporting System Information, can take on the order of seconds, which is a very long duration in the context of modern wireless communication networks. During this time, the UE is “cut off” from the network on its primary downlink/uplink carriers, which can result in significant throughput interruptions.
The Background section of this document is provided to place embodiments of the present invention in technological and operational context, to assist those of skill in the art in understanding their scope and utility. Unless explicitly identified as such, no statement herein is admitted to be prior art merely by its inclusion in the Background section.